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BUG: KCSAN: data-race in n_tty_receive_buf_common / n_tty_receive_buf_common

write to 0xffffc90000f15018 of 8 bytes by task 8313 on cpu 0:
 echo_char drivers/tty/n_tty.c:844 [inline]
 n_tty_receive_char_fast drivers/tty/n_tty.c:1448 [inline]
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1609 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0x13bc/0x1e70 drivers/tty/n_tty.c:1742
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1771
 tiocsti drivers/tty/tty_io.c:2196 [inline]
 tty_ioctl+0x8cd/0xfc0 drivers/tty/tty_io.c:2572
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0xc9/0x130 fs/ioctl.c:760
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:760
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffc90000f15018 of 8 bytes by task 11660 on cpu 1:
 add_echo_byte drivers/tty/n_tty.c:843 [inline]
 echo_char drivers/tty/n_tty.c:949 [inline]
 n_tty_receive_char_fast drivers/tty/n_tty.c:1448 [inline]
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1609 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0x1381/0x1e70 drivers/tty/n_tty.c:1742
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1777
 tty_ldisc_receive_buf+0x61/0xf0 drivers/tty/tty_buffer.c:461
 paste_selection+0x203/0x2f0 drivers/tty/vt/selection.c:408
 tioclinux+0xe5/0x450 drivers/tty/vt/vt.c:3068
 vt_ioctl+0x289/0x21b0 drivers/tty/vt/vt_ioctl.c:372
 tty_ioctl+0x9d9/0xfc0 drivers/tty/tty_io.c:2656
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0xc9/0x130 fs/ioctl.c:760
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:760
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11660 Comm: syz-executor.3 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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